Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $93.28   12.417%   $104.8626   $104.86   $104.85   $104.90  
  Purchase #2 $200.38   6.424%   $213.2524   $213.25   $213.25   $213.30  
  Purchase #3 $166.81   5.426%   $175.8611   $175.86   $175.85   $175.90  
  Purchase #4 $56.26   9.304%   $61.4944   $61.49   $61.50   $61.50  
  Purchase #5 $145.46   5.736%   $153.8036   $153.80   $153.80   $153.80  
  Purchase #6 $28.43   13.228%   $32.1907   $32.19   $32.20   $32.20  
  Purchase #7 $8.55   4.447%   $8.9302   $8.93   $8.95   $8.90  
  7 purchase totals = $699.17       $750.3950   $750.38   $750.40   $750.50